Sleep Calculator
Find the best times to go to bed or wake up so you finish a full sleep cycle.
About the Sleep Calculator
Sleep runs in cycles of roughly 90 minutes, moving from light to deep sleep and REM. Waking at the end of a cycle usually feels easier than waking from deep sleep. Five or six cycles (7.5 or 9 hours) suit most adults; the American Academy of Sleep Medicine recommends 7 hours or more.
The formula
Bedtime = wake time − (cycles × 90 min) − time to fall asleep
Worked example
Example: Go to bed at = 9:13 pm or 10:43 pm
- Inputs: I want to: Wake up at; Time: 06:30; Minutes to fall asleep: 17 min.
- Formula: Bedtime = wake time − (cycles × 90 min) − time to fall asleep
- Result: Go to bed at = 9:13 pm or 10:43 pm
Things to keep in mind
- Cycle length varies from about 70 to 120 minutes between people and through the night.
Questions people ask
How much sleep do I need?
Adults: 7–9 hours. Teens: 8–10. School-age children: 9–12.
Why do I feel groggy after 8 hours?
You may have woken mid-cycle, or not had enough consistent sleep over the week.